This application represents a request for supplemental funds to support the addition of a new project to an existing program project. Project 5 concerns the role of cell cycle regulators in granule neuron proliferation and in medulloblastoma cells from Drs. Martine F. Roussel and Charles L Sherr. The goal of the original program project is to increase understanding of the molecular basis of normal and neoplastic growth in the developing brain. The ultimate objective is to use this knowledge to devise novel strategies for treatment of medulloblastoma, the most common pediatric malignancy of the central nervous system. This objective is being pursued through four interactive projects that investigate the role of different signaling pathways in the growth of the central nervous system and brain tumors supported by an Administrative Core and a Bioinformatics and Microarray Core. In Project 1, T. Curran utilizes a mouse model of medulloblastoma to investigate the role at the Shh/Ptc/Smo pathway in tumorigenesis. This involves the use of pharmacological inhibitors in cell culture and in viva, a molecular characterization of Glil and comparison of the epigenetic and genetic alterations underlying medulloblastoma by nuclear transplant into oocytes. In Project 2, P McKinnon investigates the contribution of DNA damage signaling to medulloblastoma formation. This project is based on the characterization of a novel model for medulloblastoma in mice lacking DNA Ligase IV and p53. This analysis will involve comparison of gene expression microarray profiles of the different medulloblastomas in the program. In Project 3, R. Gilbertson is investigating the role of ERBB2 in human medulloblastoma. This involves the characterization of human medulloblastoma cell lines using pharmacological and gene expression microarray approaches. The information will be compared to the data obtained on mouse models and an existing i database of human brain tumors. A mouse model will be created in which ERBB2 is expressed in cerebellar granule neurons. In Project 4 S. Baker is studying the role of the Pten signaling pathway in growth regulation in the brain. This includes characterization of the function of downstream effector genes in the cerebellum and the creation of new mutant mouse strains to investigate its contribution to growth, proliferation an, tumorigenesis.